1. Field of the Invention
The present invention relates to a light emitting device comprising light emitting elements each including a pair of electrodes and a light emitting layer sandwiched between them, and a manufacturing method of the same. More particularly, the invention relates to a circuit configuration and a sealed structure of the light emitting device.
2. Description of the Related Art
In recent years, display panels using light emitting elements are actively developed. A light emitting element comprises a pair of electrodes (anode and cathode) and a light emitting layer sandwiched between them. The light emitting layer emits light when a voltage is applied to both electrodes. Since a display panel using the light emitting elements emits light in its light emitting layer sandwiched between both electrodes, further downsizing and thinner shape of the display panel are expected to be achieved.
As an obstruction to the downsizing and thinner shape of a display panel, an external circuit is noted. When forming a circuit externally, it becomes difficult to achieve the downsizing and thinner shape of a display panel since a wiring such as an FPC (Flexible Printed Circuit) for connecting the circuit to a substrate over which a pixel portion is formed is required as well as the mounting of the circuit.
It had been difficult to integrally form a signal line driver circuit, a signal processing circuit, and the like on the same substrate with a pixel portion by using conventional TFTs (Thin Film Transistors) formed of amorphous silicon since it has low mobility. However, at present, a semiconductor layer having high mobility can be formed by using low-temperature silicon at a relatively low temperature, thus it is possible to integrally form these circuits and the pixel portion on the same substrate. For example, as shown in FIG. 9, signal line driver circuits 901 and 902, and a signal processing circuit 903 are all formed on a substrate 905 which is connected to an FPC 904. Reference numeral 907 denotes a sealant and 908 denotes a sealing substrate to seal a light emitting element off. By integrally forming these circuits and a pixel portion 906 on the same substrate in this manner, no external component is required, which realizes the further downsizing and thinner shape of a display panel.
It is needless to say that the display panel using light emitting elements is expected to be applied to a mobile terminal by virtue of the expected compact size and thinness. However, as for a display panel for a mobile terminal, it is supposed to undergo a difficult condition as compared to a stationary display panel regarding the case of the outside use in wet weather, danger of a drop, and the like. Therefore, the downsized and thinner display device is required to have a high reliability enough to prevent the deterioration or breakdown even under such a difficult condition.
However, the light emitting element is easily deteriorated by moisture, oxygen, and the like as its light emitting layer comprises an organic material or an organic material partially including an inorganic material, which may generate a dark spot or shrink.
In order to prevent such a problem, there is a method in which light emitting elements formed on an insulator are sealed hermetically with a sealant and a covering material each formed around the light emitting elements, and a filling material such as a resin is provided around the sealed space and the covering material, thereby blocking out oxygen and moisture (see Patent Document 1 for example).
[Patent Document 1]
Japanese Patent Laid-Open No. Hei 13-203076
However, even by adopting such a method, the reliability which is required for the downsized and thinner display panel has not yet been secured enough so far.